Combined reduction and reversing gearing



Feb. 21, 1939. s. L. WILLIAMS 2,148,313

- comsINED REDUCTION AND REvEasING GDARING- Filed April 8. 195e /4 56 oz n l 5" )a n L1 ATTORNEY Patented Feb. 21, 1939 PATENT ori-Ice CQMBINED REDUCTION AND BEVERSNG GIEARINGI George L. Williams, Hartford, Conn., assignor to United Aircraft Conn., a corporation of Delaware Corporation, East Hartford,

Application April 8, 1936, Serial No. 73,287 Claims. (Cl. 'I4-305) This invention relates to improvements in combinedreduction and reversinggearing for driving two rotating bodies in opposite directions at a speed different from the speed of the driving 5 power plant.

The invention has particular application to gearing' for driving coaxial oppositely rotating aeronautical propellers where both are driven by the same engine and has for anA object the pro- `10 vision of a combined reduction kand reversing gearing of the character described wherein the tooth loads` on the various gears are maintained at an unusually low value. d A further object resides in lthe provision of l5 a system of gearing of the character described which is light in weight and occupies a small space so that it may be conveniently disposed within the front portion of an internal combustion engine of the type usually employed for the propulsion of airplanes.

Other objects and advantages will be more particularly pointed out or will become apparent as the description proceeds.

-In the accompanying drawing, in which like reference numerals are used to designate similar parts throughout, `there is illustrated a suitable mechanical embodiment of what is now considered to be the preferred form of the invention. The drawing, however, is for the purpose of illustration only and should not be taken as limiting the invention, the scope of which is to be measured entirely by the scopel of the appended claims.

In the drawing, i Fig. 1 is a longitudinal sectional view of the front portion of an engine, and a reversing gear unit constructed according to the idea of this invention. s

Fig. 2 is a diagrammatic illustration showing the power distribution through the gear unit and the forces acting upon thevarious elements of the gear train.

Referring to the drawing in detail, the numeral In generally indicates the front portion or nose section of an engine such as a radial internal combustion engine conventionally employed for the propulsion of airplanes. This nose section serves as a casing for the combined reduction and reversing gear unit and also serves as a load transferring member for'receiving the thrust developed by the propellers and transmitting this thrust to the engine, from which it is transmitted to the airplane. The numeral l2 designates the engine crankshaft which is provided with a 'crank i4 and a hollow frontend lli formed with ex- 65 ternal splines lt. The front end of the crankshaft is supported in antifriction bearings 2|] and 22 which. are seated in vpartition members 24 and 26 respectively secured to the engine crankcase The two oppositely rotating propellers are sup- 5 ported upon and driven by -propeller shafts 30 and 32. Both-cf these shafts are coaxialjand the shaft 32 is constructed as a .sleeve which surrounds a. portion of the hollow inner shaft 30. Both shafts extend forwardly from the front por- 10 tion of the engine and support the two propellers in cantilever relation. y A

At its forward 'end the shaft 30 is provided with a set of external splines 34 for maintaining the propeller which it carries against'rotation with 16 respect thereto, and with an annular wedge member 36 for receiving and centering the rear end of the propeller hub. A similar wedge member centers the front end of the propeller hub and retains the propeller upon the shaft through the `20 medium of a nut screw'threadedupon the end of the shaft and bearing against the wedge member. As such devices for securing propellers upon propeller shafts are old and well known in the art, it is believed that a detailed description 25 or illustration thereof is not necessary for the purpose of this disclosure.

The outer shaft 32 which carries the rear pro` peller is also provided with splines 38 and with a r'ear annular wedge member 40 for centering the 30 rear end of the propeller hub. The propeller is retained upon the shaft and the forwardV end thereof centered with respect to the shaft by means of a combined nut and wedge member 42 screw threaded upon the forward end of the shaft 35 32. 'Ihis member 42 is provided with a forwardly extending portion which overlies and receives the outer race of `an anti-friction thrust bearing 44 disposed between the shafts 30 and 32, the inner race of this bearing being secured between the 40 annular wedge member 36 and an annular shoul-` der 46 formed on the exterior of the inner shaft 3l).v This bearing 44 restrains the two shafts 30 and 32 against radial or axial movement with respect to each otherv while permittingfree rela- 45 tive rotation.

While the lnut and wedge element 42 has been. illustrated as a single piece, it is obvious that this member may be divided into a plurality of separate elements if desired, and may be provided with 50 suitable shoulders or other means to definitely determine its assembled'position with respect to the shaft 32 and the bearing 44.

Formerly the general practice was to mount the propeller directly upon the engine shaft and sembly. -The cage is hence to drive the propeller at the same speed as the engine, but it has been found that material advantages are obtained by driving the propeller at a slower speed than the operating speed of the engine and for this reason it is the present practice, especially in the-case of engines of large power output, to interpose a suitable reduction gear between the engine crankshaft or drive shaft and the propeller shaft. In the case of two propellers mounted to rotate in opposite directions about the same axis, it is also necessary to provide suitable means for givingto one of the propellers a direction of rotation opposite to the direction of rotation of the engine. Furthermore, particularly in the case of military airplanes, it is highly desirable that the rotation of both propellers be accurately timed in order that a machine gun may be fired through the propeller disc without interference between the projectiles and the propeller blades. The present combined reduction and reversing gear unit accomplishes these various results and at the same time has the advantages of light weight, small volume and low tooth loading as set forth'in the objects as stated above.

An external ring gear 48 forward end of the drive a bell housing 58 having a tubular shaft portion 52 provided with internal. splines which engage with the splines I8 and extending rearwardly is mounted upon the to a location in which it bears against the forward face of the inner race of the anti-friction bearing 22. The inner race of the antifriction bearing 28 is carried by the shaft portion 52 of the bell this shaft portion by means of suitable annular shoulders or other means. For purposes of manufacture and assembly the external ring gear 48 is made separately from the bell housing 58 and is connected thereto by suitable means such as the bolts 84.

The propeller shaft 88 is provided at 'its rearend with a reduced portion 58 which extends within the hollow forward portion I8 of the crankshaft I2 to provide a spigot bearing between these two coaxial shafts; preferably, a plain bearing 58 is interposed between the rear end of the shaft 88 and the forward end of the crankshaft I2. Intermediate its length the shaft 88 is provided with a plurality of outwardly extending` arms 88 connected by outwardly extending ange portions 82 to provide one side of a gear carrying cage generally indicated as 84. This cage portion may either be formed integrally with the shaft 88 or may be made separately and rigidly secured thereon as may be desired for convenience in manufacture and ascompleted by means of a forward portion 88 bolted or otherwise suitably secured to the rear portion 82.

The cage 84 carries a plurality of radially spaced spur planetary gears, 'one of which is indicated at 88. These gears 88 areprovided with gear teeth which engage with teeth 18 provided aroundthe interior of the ring gear 48 and at the same time engage with teeth 12 provided upon the rear end of the outer propeller shaft 82 or upon a sun gear member rigidly secured' to the rear end of this shaft.

From the above description it will be observed that as the crankshaft I2 rotates the ring gear 48, a driving force will be applied to the radially outward portion of each of the planetary' spur gears 88. This force will be transmitted to the pins, one of which is Indicated al; 1l, 71.11911 $11?.-

shaft I2 by means of housing and is located upon Amay be Agears 68 to the gear teeth 12 and this reaction force will cause the outer propeller shaft 32 to tend to rotate in a direction opposite to the direction of rotation of the shaft 38. Thus, this much of the gear unit would cause. the two propellers to be driven in opposite directions with respect to each other. This, however, would be a primary differential drive and the speeds of the two propellers would be variable and proportional to the power absorbed by each and the rotation would therefore not be definitely timed.

The cage 84 is. provided with an annular bevel gear 16v and the shaft 32 is provided with a similar annular bevel gear 18 which faces the gear 16. If it is desired that the two propellers as indicated at 88 and 82 in Fig. 2 rotate at the same speed the gears 16 and 18 will have the same radius, but, if it should be desired that the two propellers should rotate at different speeds, the radii of the gears 16 and 18 will be proportioned accordingly. In the form of the invention illustrated, it has been assumed that the two propellers will rotate at the same speed and the gears 16 and 18 have therefore been illustrated as having the same radius and, for convenience, this form of invention will be particularly described, it being understood that the invention is not specifically limited to a construction in which the two propellers rotate at exactly the same speed.

Between the gears 18 and 18 there is provided a plurality of beveled pinion gears 84 mounted to rotate on :fixed pins 86 mounted in a fixed cage 88 secured at the forward end of the gear casing I8 by suitable means such as the cap screws 88. 'Ihe gears 84 will be referred to hereinafter as the idler gears. The gears 16 and 18 and 84 serve to transmit a portion of the torque applied to the cage by the planetary gears 88 from the cage to the shaft 32 to equalize the torque supplied to the propeller shafts 88 and 82 and cause these two shafts to rotate at a predetermined speed in opposite directions as will be more specifically pointed out in the de- ;iption of the force diagram illustrated' in Both propeller shafts 88 and 32 are supported and centered in the gear case I8 by means .of a ball thrust bearing 82 disposed between the outer shaft 82 and the forward end of the gear casing. The outer race of this ball thrust bearing secured in the gear casing by means of tle cap screws 88 which support the fixed cage 88. The inner race is secured upon the shaft 82 by means of a nut 84 which holds the inner race against an annular shoulder 88 provided on'the shaft.' The centering and the supporting action of the thrust bearing 82 is transmitted to the inner shaft 8l through the outer shaft 32 and the ball thrust bearing 44. Lubricant or hydraulic fluid may be supplied to the spacebetween the two propeller shafts by means of an oil collector ring 88 mounted upon, the fixed cage 88 and overlying the inner ends of the pins or axles 88. -The lubricant or hydraulic uid may be led to the collector ring through suitable channels provided in the fixed cage 88 and is led through suitable apertm'es |88 in the ring to a channel |82 in the inner side of the ring from which it is led 7 sent imaginary links between these various gear.

`agi-rams A throughapertures |04 in the outer shaft to the space between the shafts. Seal rings |06 are providedvat each sideof the collector ring between the ring and the outer shaft and a plain bearing |08 between the two propeller shafts serves as a seal to prevent the lubricating or hydraulicv fluid from leaking out of the space between the shafts at the rear end of the space.

Referring now to Fig. 2, thev heavy vertical lines refer to various elements of the gear train illustrated in Fig. 1,-and the dotted lines repreelements. The figure representsv an instantaneous force analysis of the gear train and the forces have been considered as applied in a direction to rotate the various gear elements toward the left about their various centers indicated as CI, C2, C3, etc.` The continuous light line'represents the flow'of power or the power distribution through the, various gear elements, and therarrows labeled F, Fl, F2, etc. indicate the forces acting upon the teeth'and mounting pins of the various elements. The arrows labeled T| and T2 indicate the torque applied to the respective propeller shafts. v'

Considering first the power distribution, itwill be observed that the power ow originates, for the purpose lof this disclosure in the drive shaft I2, and flows through the ring` gear 48 to the outer portion of the planetary gears and only one ofthe plurality of idler gears is considered, From the outer portion of the planetary gears the power flows tothe cage carried -pin 14, and to the inner portion of the planetary gear and from thence to the sun gear 12 from which it flows to the outer propeller shaft 32. The power flowing to the cage carried pin is divided, a portion thereof .flowing through the cage to the inner propeller shaft 38, and another portion ilowing to the beveled ring gear 18 and from there through the reversing idler Vgear 84 to the beveled ring gear 18, from whence it flows to the outer propeller shaft 32 and is added to the power transmitted to this propeller shaft through the sun gear 12.

The tooth and pin loads are represented by the arrows and their definitions have been indicated by symbols placed beneath the various arrows indicating the forces. The first force essential to this construction is the force F2 exerted by the ring gear upon the outer portion of the planetary gear and this force is shown to be considerably less than the corresponding force FI exerted by thev drive shaft |2 for the reason that F2=F1(1'/1'1) and the factor Jr1 is less than 1. This force'F2 is also, of course: proportional to lthe number of planetary gears used in the gear train, the construction thus tending to keep the tooth loads between the ring gear and the planetary gears Very low. As the planetary gear is free to rotate aboutI its axis the load F3 between the inner portion of the planetary gear and the sun gear 12 will be the same as the load F2 between the ring gear and the outer portion ofthe planetary gear, and will be correspondingly low. The force F4 exerted by the planetary gear upon the cage carried pin, 14 will be equalto the sum of the loads` F2 and F3 between tlle planetary gear and the ring gear and the sun gear, but this force is divided before it is applied to any other gear element and only the portion indicated-at F is applied to the idler gear 84. This force which is equal to the portion of the drive shaft force FI determined by the number of idler gears times 18 is the same as the force F5 and is also correspondingly low. The forcel F1 exerted by the idler vgear upon its fixed pin 86 will be the sum vof the forces F5 and F6, since the idler gear is free to rotate about its maintaining. pin. Thus,

4 because the ring gear-has a large radius and the planetary' gears are mounted upon a movable cage, the tooth loads between the ring gear and' the planetary gears will be low and, becausethe force transmitted from the planetary gears to the inner propeller shaft goes directly through the pins 14 and cage 50 without involving any addi-1 i tional gears and because the force transmitted from the planetary gears to the outer propeller shaft 32 is divided so that a portion of it goes through the sun gear 12 and another portion goes through the beveled ring gears 16 and 18, and the idler gear 84, the tooth loads on all of the gears are maintained at very low values. The beveled ring gears 16 and 18 are made with the maximum diameter possible in view of the restrictions imposed by the shape of the gear case I0 so that the tooth loads between these ring gears and the idler gears may be further decreased.

For a gear train of the form illustrated the forces acting on the various gears and the resulting torques imposed on the propeller shafts may be stated as follows:

' F1=Force exerted by\ drive shaft divided.

F2=F1(T/1'1) F3=Fz F4=F2+F3 F5 :F1 (H274) Fe=F5 Fv=F5lFsWhere the two propellers rotate at the same speed in opposite directions.

From the above description, the relation of the various gear elements to each other will be clearly apparent and it will also be observed that by means of the form of gear train illustrated, the two coaxial propellers will be rotated in timed relation with respect to each other in opposite directions, and at the same time the tooth loads on the various gears will be maintained at an extremely low value. Also the particular distribution of forces permits the use of relatively small light gear elements arranged in a compact manner to provide a light unit of small dimensions for the purpose indicated.

The nose section ||l is separable from the engine along with the partition 24, both of these `elements being detachably secured to the engine by suitable means such as the cap screws ||||,A

The propellers, the propeller shafts-32 and 34, and the entire gearing assemblyvare carried by the nose section and the partition 2 4 so that the entire propeller andA gear unit may be removed from the engine with the nose section and may be assembled in the nose section and applied to the engine as a unit.

While there has been illustrated and described a particular mechanical embodiment of the idea of the invention, it is to be understood that the invention is not limited to the particular mechanical embodiment so illustrated anddescribed, but that such changes in the size, shape, and arrangement of partsmay be resorted vto as come within the scope of the appended claims.

As the invention has now been described so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows.

I claim:

, l. In a combined reversing and reduction gearing for transmitting power from a single drive shaft to a pair of coaxial driven shafts turning in opposite directions at a speed less than thespeed oi' the drive shaft, an external ring gear carried by said drive shaft, a cage carried by one of said driven shafts, a sun gear carried by the other of said driven shafts, planetary gears carried by said cage meshing with said external ring gear and said sun gear, a beveled ring gear carried by each of said driven shafts, and beveled pinion gears mounted to turn about fixed axes meshing with said beveled ring gears.

2. In a combined reversing and reduction gearing for transmitting power from a single drive shaft to a pair of coaxial driven shafts turning in opposite directions at a speed less than the speed of the drive shaft, a ring gear on said drive shaft, planetary gearing between said ring gear and said driven shaftsY acting on said driven shafts through unequal moment arms to apply unequal torques in opposite directions to. said driven shafts, and speed equalizing gearing connected directly between' said driven shafts.

3. In a combined reversing and reduction gearing for transmitting power from a single drive shaft to a pair of coaxial driven shafts turning in opposite directions at a speed less than the speed of the drive shaft, a ring gear operatively connected with the drive shaft, planetary gearing between said ring gear and said driven shafts including a planet gear carrying cage on one driven shaft and a planet gear other of said driven shafts applying unequal torques in opposite directions to said driven shafts, and speed equalizing gearing connected directly between said driven shafts.

4. In a combined reversing and reduction gearing for transmitting power from a single drive shaft to a pair of coaxial driven shafts turning in opposite directions at a speed less than the speed of the drive shaft, a ring gear on said drive shaft, planetary gearing between said ring gear and said driven shafts applying unequal torques in opposite directions to said driven shafts, and speed timing gearing between said driven shafts, comprising, a beveled ring gear on each shaft, and a beveled pinion mounted on a fixed pin meshing with said beveled ring gears.

5. In a combined reversing and reduction gear for transmitting power from a single drive shaft to a pair of coaxial driven shafts turning in opposite directions, a planetary gear train comprising a ring gear driven by the driven shaft, planet gears supported on one driven shaft, and a. sun gear on the other driven shaft, for receiving power at high speed and low tooth loads from said drive shaft and dividing said power between said driven shafts so that the major portion of the power is transmitted through the bearing pins of said planetary gears to one of said driven shafts and a minor portion thereof is transmitted through the gear teeth to the other of said driven shafts, and a second set of gears between said driven shafts for equalizing the power supplied to said shafts from said drive shaft.

GEORGE L. WZDILIAMS.y

driven inner gear on the 

